Binoculars or binocular telescopes are a pair of identical telescopes mounted side-by-side and aligned to point accurately in the same direction. Binoculars allow the viewer to use both eyes when viewing distant objects. Furthermore, binoculars give viewers a three-dimensional image: for nearer objects the two views, presented to each of the viewer's eyes from slightly different viewpoints, produce a merged view with an impression of depth.
Binoculars are used by hunters, bird watcher, and other nature enthusiasts. By design, binoculars are intended for viewing distant objects. However, it will be desirable if the viewer can use his binoculars not only for viewing distant objects but also for viewing objects as close as one meter. This will allow the viewer to use his binoculars for observing many interesting objects such as outdoor plants, flowers, butterflies, dragonflies, etc.
Humans have two eyes with overlapping visual fields that use parallax to gain depth perception. Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the convergence angle between those two lines. Nearby objects have a larger parallax than more distant objects.
When an object at a close distance is viewed through binoculars, parallax may become too large. This is because the apparent convergence angle, i.e. the angle of the light beams exiting from the right and left eyepiece lenses, is magnified by the binoculars. For example, when an observer views an object at a distance of one meter using binoculars having a magnification of 10×, the observer needs to turn his eyes inward (make the eye axes converge) so much as if viewing an object at a distance of 10 cm. This excessive parallax greatly strains the observers eyes. In such a situation, many people simply cannot merge the right and left images into one.
Several approaches have been taken in the prior art to reduce the excessive parallax produced by binoculars when viewing close objects. U.S. Pat. No. 4,264,122 issued on Apr. 28, 1981 to Schmidt et al. teaches a binocular telescope wherein the angle between left and right telescopes' optical axes can be adjusted using an articulating hinge mechanism. An alternative solution is disclosed in U.S. Pat. No. 6,134,048 issued on Oct. 17, 2000 to Kato et al. wherein the excessive convergence angle is corrected by a mechanism that decanters an element of the objective lens system.
While it is advantages to reduce parallax when viewing nearby objects, in some other applications it might be desirable to increase the parallax between the left and right images. For instance, when observing objects located several hundred meters or more, increasing parallax helps provide an enhanced three-dimensional viewing experience. It is also possible to increase the horizontal field of view of binoculars by making the left an right telescopes have divergent fields of view.
The present invention introduces a novel solution for correcting or adjusting the convergence angle in binocular telescopes: A pair of wedge prisms are introduced in the optical path of the left and right telescopes to optically steer their fields of view. Parallax correction can be applied to binoculars' real field of view (objective end) or to their apparent filed of view (eyepiece end).